1. Technical Field
This invention relates to a wound golf ball of consistent quality featuring distance and controllability.
2. Prior Art
Wound golf balls are generally classified into two types, solid center balls and liquid center balls. The solid centers are generally formed by molding high cis-polybutadiene base compounds, which are crosslinked with metal salts of unsaturated carboxylic acids such as zinc acrylate or sulfur. The liquid centers are generally formed by filling center bags of natural rubber base compounds with a liquid such as water or barium sulfate paste.
For improvements in wound golf balls, a number of proposals have been made with respect to the compounds and geometry of centers. For example, JP-A 51544/1990, 192512/1994, 299052/1994, and 504308/1994 disclose thermoplastic polyester elastomer base compositions of which solid centers are molded. JP-A 159285/1990 discloses a golf ball core stock containing more than about 50% by weight of a fluoro-resin.
In most molding processes, the number of cavities in a mold is increased from the standpoint of production yield. Typically about 20 to about 50 solid centers are prepared per mold. When the solid centers prepared from a single mold are compared, substantial variations are found among them with respect to hardness, weight and outer diameter. These variations among solid centers have a substantial influence on the weight and hardness of balls prepared therefrom, becoming a bar against the mass-scale production of balls of consistent quality.
Also, for improvement in golf balls, a number of modifications have been made on the cover stock. For example, JP-B 44303/1993 discloses a cover stock comprising an ionomer resin loaded with an inorganic white pigment containing at least 60% by weight based on the white pigment of barium sulfate having a particle size of 1 to 10 .mu.m. Japanese Patent Application No. 76557/1997 discloses a multi-layer cover including a first cover layer based on a thermoplastic polyurethane and a second cover layer based on Surlyn.
Under these circumstances, the wound golf balls are required not only to solve the problems associated with the solid center, but also to form an appropriate cover.